Shadow mask frame of sintered material for color tubes

ABSTRACT

A frame that rims and mounts a shadow mask in a color television picture tube is fashioned by casting in integral form, and is preferably sintered from a powder metal base to provide a porous metallic material easily degassed and light in weight. The rim member has a cross section of varying thickness and shape disposed in a general L-shaped pattern and may have strengthening gussets disposed at predetermined positions about the periphery. Optionally integral mounting members such as brackets may be formed at selected positions about the periphery, or they may be affixed by conventional methods to a simple rim member comprising a closed loop of framing material around the periphery of the mask.

United States Patent 7 Inventor Jay Johnson 3,351,996 11/1967 Fiore 313/85S X b 3,376,451 4/1968 Mears 313/92B 2 APPL 744,937 3,387,159 6/1968 Schwartz et al.... 313/92BX [22] Filed July 15,1968 FOREIGN PATENTS [451 Patented Mar-9,1971 1,236,556 3/1967 Germany 3l3/85S [73] Assignee Kentucky Electronics Inc.

Owensboro, KY Primary Examiner-Robert Segal Attorney-Laurence R. Brown [54] SHADOW MASK FRAME OF SINTERED MATERIAL FOR COLOR TUBES 4 Clams 1 Drawmg I ABSTRACT: A frame that rims and mounts a shadow mask in [52] U.S.Cl 313/85, a color television picture tube is fashioned by casting in in- 313/311 tegral form, and is preferably sintered from a powder metal [51] Int. Cl ..H0l j 31/20, base to provide a porous metallic material easily degassed and H01 j 29/02, H01 j 29/06 light in weight. The rim member has a cross section of varying [50] Field of Search 313/85 (5), thickness and shape disposed in a general L-shaped pattern 92 and may have strengthening gussets disposed at predetermined positions about the periphery. Optionally integral [56] References Cited mounting members such as brackets may be formed at UNITED STATES PATENTS selected positions about the periphery, or they may be afiiited 2,164,699 7/1939 Clark 313/41 y Conventional methods to a simple rim member comprising 2,795,713 6/1957 Van Hekken et a1. 313/92BX a closed loop of framing material around the periphery of the 2,897,392 7/1959 Fiore 3 13/923 mask PATENTEDHARQIQYI I 3569759 INVENTOR JAY H. JOHNSON BY M/AW @M m ATTORNEY SEADOW MASK ME F SINTERED MATERIAL FOR COLOR TUBES This invention relates to shadow mask-type color picture tubes and, more particularly, it relates to frames for holding and mounting shadow masks within cathode-ray tubes.

It has become conventional in this art to mount a thin perforated shadow mask upon a heavier framework which comprises a rim surrounding the periphery of the shadow mask generally conforming in shape with the surface of the picture tube screen. These rims have been manufactured generally by two different processes. A first process constitutes forming and bending an endless steel strap into a loop, cutting the strap and welding the ends together. A second process constitutes stamping of a rim from a steel plate and bending the rim in appropriatedies to assume the necessary shape.

In order to appreciate the problems posed by these prior art construction techniques, the operational requirements of a shadow mask and frame within a picture tube need be considered. Since high voltages are found in the tubes and electron beams of high potential and kinetic energy impact, the shadow mask, burrs and sharp edges present many corona problems and even possibilities of X-ray radiation. Also, a high vacuum and absence of any materials contaminating chemicals in cathodes and phosphor screens must be maintained within a large volume tube, so that any entrapped gases or contaminating materials must be eliminated. High electron beam impact energies and high temperatures may tend to release contaminatory substances from the frame materials. In this respect great care must be takento remove rust, scale, chemicals and burrs from finished frames. Many commercial grades of steel that can be formed in the manner stated are difficult to degas and decontaminize. This becomes a significant problem whenever stampings and weldings occur, and where any chemical treatment is required to remove welding scale, rust or to temper stampings. Processing procedures thus require many steps in deburring, neutralizing chemicals, removing scale, heat treating, and the like. Such processing is complicated by the large mass of metal required in a shadow mask frame. This, in part, results since the metal thickness must be s'ufficient to overcome the point of greatest stress. This adds to the weight, also an undesirable feature as well as the cost of materials and inefficiency.

Furthermore, extremely precise tolerances must be maintained for both electrical and mechanical registration purposes within the tubes, whichexhibit convergence problems magnified whenever any distortions occur in the shadow mask surface. These are amplified whenever heating or aging tend to relieve stresses incurred in shaping sheet materials to result in dimension changes by means of elastic or thermal deformations. Thus, the prior art techniques have not been found to satisfy the needs for precision in the manufacture of the critical parts to which this invention is directed.

it is therefore a general object of this' invention to provide improved shadow mask mounting frames correcting some of the foregoing problems existing in the prior art.

It is another object of the invention to provide shadow mask frames having precise dimensions with dimensional stability.

A further object of the invention is to provide improved shadow mask frames which do not tend to contaminate cathode ray tubes with chemicals or gases.

Still another object of the invention is to provide improved shadow mask frames which are readily degassed.

Yet another object of the invention is to provide improved shadow mask frames easily manufactured by simple methods.

Another object of the invention is to provide an improved shadow mask frame light in weight and using a minimum amount of material.

Therefore in accordance with this invention there is provided a shadow mask frame constructed in optimum shape and strength by means of' casting, preferably in powdered metallurgy form to provide asintered porous metal which is more readily degassed and can be held to high purity without contaminating impurities. Thus, the shape of a typical rim loop member can vary not only about its generally L-shaped cross section pattern to give added strength with less weight, but it can also be shaped pr gusseted about its loop at selected mask peripheral positions. Other cross section configurations can be used. By casting, the frame has rounded edges, not necessitating deburring operations and not conducive to corona and X-ray generation. A single unitary integral member is thus formed which can include mounting structure or brackets if desired, which can be held precisely to shape matching a complex three-dimensional surface of a color tube screen.

Further features and objectives of the invention are found throughout the remaining specification, which refers to the accompanying drawings illustrating preferred embodiments of the invention, wherein:

FIG. 1 is a partial elevation view, partly in section, of a color picture tube embodying a shadow mask frame constructed in accordance with this invention;

FIG. 2 is a plan view of a typical shadow mask frame constructed for a rectangular picture tube;

FIG. 3 is a cross section view of the generally L-shaped pattern of the shadow mask frame construction afforded by this invention;

FIG. 4 is a cross section view of a further pattern of a shadow mask cross section illustrating rounded corner construction and gusseting techniques;

FIG. 5 is a perspective view of a rim section; and

FIG. 6 is a top view of the construction shown in FIG. 2 having an integral flange thereon for shielding the beam.

A view of the shadow mask and mounting frame positioned within a color picture tube 10 is shown in FIG. 1, where the dimensions of the mask and frame are exaggerated to show constructional details. A shadow mask 11 of thin metal with perforations 12 is disposed to conform with the shape of the tube face 14 and the phosphor screen 15. This mask 11 is disposed upon a metallic frame 16 which has a cross section 17 shaped somewhat like an inverted J to form an electron beam shield projection 18. Integral mounting members 19 may be formed integrally upon the frame 16 or may be attached thereto for holding the shadow mask ll in proper position near the face 14 of cathode ray tube 10. The frame 16 is affixed to the mask about the periphery by suitable techniques such as welding.

A typical plan view for a rectangular tube is shown in FIG. 2, with corresponding cross section views of two different configurations shown in FIG. 3 and FIG. 4 such as might be seen by looking to the right respectively from intersection lines 3-3 As may be visualized from comparing FIGS. 1 and 2 the frame 16 which forms a rim member about the periphery of the mask 17, has a complex curvature depending upon the design of the corresponding picture tube screen to which it conforms. This curvature may be attained by casting in a single unitary integral piece the entire frame 16. Dies may be made to conform to one of the cross sections of FIGS. 1, 3 and 4 as desired. It is noted that the cross section l7 for example in FIG. 3 is filletted to give extra strength at the intersection of the two arms of the L-shaped pattern. This provides for a varying thickness cross section disposed in a generally L-shaped pattern where one arm conforms in contour with the surface area of the shadow mask about the periphery (FIG. l).

As shown in FIG. 4, gussets 20 may be provided to strengthen the rim member at predetermined positions of the rim member loop located about the periphery. This permits the entire cross section 17" to be of smaller area, and thus the frame 16 to be lighter in weight and have less metal to require degassing, since it need only bear the lighter loads away from the gussets 20. As seen in FIG. 4, the casting can permit rounding of all the corners as at 21, 22 so that burrs and corona problems are eliminated. Punching, bending and shaping sheet metal require operations in contrast that tend to create burrs and dents and generally require a deburring step.

Another manner of increasing strength while retaining a frame of minimum weight is to vary the density of the frame at positions needing greater strength or closer dimensioning. This, in essence, is done from a metallic material of relatively low density formed from a powdered metal compact by a selective coining operation with dies engaging the rim member after the sintering at those portions requiring more strength in a given direction or closer dimensional tolerance than attainable simply by the sintering process.

Preferably the frame 16 is cast or pressed of a powdered metal substance and is curved by sintering to form a porous metallic material, which is easier to degas in the baking out process necessary in high vacuum tubes. In such a powder metallurgy process, which may conform with known techniques in general, several other advantages occur, since reheating for tempering is not necessary and no scaling or burring results from welding or mechanical dies operating upon hardened steel to shape it. Also, the mass is a function of density so that the porous sintered material adds greater strength at reduced weight. An effective frame of high strength can be formed by sintering by powder metallurgy techniques between 65 and 85 percent that of a solid metal. A significant advantage is the purity of metal attainable as compared with cold rolled steels and the like which may contain scales, slag and many other impurities, some of which can contaminate phosphors or emitting surfaces within a high vacuum cathode ray tube, or cause secondary emission problems when impacted by the electron beam. Since no chemical treatment steps are necessary, removal of chemicals is not a problem and the processing becomes relatively simpler. Not to be'overlooked is the efficiency of metal used with no scrap generated by cutaways or overlaps for welding. Alternatively, the frame could be cast of a suitable metal while retaining many of these advantages over prior art frames.

Accordingly, an improved frame for shadow masks in color picture tubes is provided in accordance with this invention to meet the exacting requirements of complex mechanical shaping coupled with performance with a critical electrode in a high voltage high vacuum cathode ray tube.

The composition of metal used in the frame is preferably a steel of high strength with properties such as 1010 cold rolled steel and possible with nickel added for strengthening. When powder metallurgy techniques are used, the porosity after sintering, reduced weight and the casting technique permits a design reducing the overall amount of metal used while adding strength where points of greatest demand exist, thus improving the performance in a cathode ray tube over a strap of uniform thickness and cross section. Weight is about 25 percent less than that of stampedor welded frames. Relative overall thickness of the frame may be reduced from about .010 inch to the order of .025 inch.

Greater flexibility in design of the shadow mask is also permitted by casting in a particular shape without restrictions imposed in the strap deforming or stamping methods, since a relatively fiat mask may be mounted or welded to a frame without requiring a doming operation.

In addition, as shown in FIG. 6, advantages are afforded by this invention in providing additional structure which is cast in one integral piece with the frame 17 such as shown by the flange 30 introduced to extend from the frame about its periphery to serve as an electron beam shielding member. Other such structural features of complex shape may be incorporated in the initial manufacture as desired without the necessity of extra processingsteps and complex welding or mounting steps.

Having therefore described the nature of the invention and preferred embodiments thereof setting forth its advantages and advances over the prior art, those features believed descriptive of the spirit of the invention are set forth with particularity in the appended claims.

lclaim:

1. In a color picture tube of the type in which a plurality of electro directed beams through a shadow mask to impinge upon discrete colored phosphor areas located upon the screen of the tube the combination of a shadow mask having a complex curvature conforming to the surface of the screen and a frame mounting the shadow mask by supporting it about its periphery comprising an unbroken metallic loop generally conforming in contour with the periphery of said shadow mask disposed adjacent to said shadow mask and in contact with the periphery thereof, said metallic loop comprising two arms disposed from an intersection in a generally L-shaped cross section with one arm in contact with the periphery of the shadow mask and the other arm disposed away from the shadow mask and picture tube screen, said rim member comprising sintered porous material having at various positions about said periphery a thickness of the sintered porous material in the vicinity of the intersection of the two arms differing from that at the positions of the arms more remote from the intersection.

2. Apparatus as defined in claim 1, in combination with a cathode ray picture tube having a phosphor screen disposed in a high vacuum.

3. A frame as defined in claim 1, wherein the rim member is of a porous sintered metallic structure having a density in the order of 75 percent that of a solid metal.

4. A frame member as defined in claim 1 with a one-piece rim member including bracket members extending outwardly therefrom. 

1. In a color picture tube of the type in which a plurality of electro directed beams through a shadow mask to impinge upon discrete colored phosphor areas located upon the screen of the tube the combination of a shadow mask having a complex curvature conforming to the surface of the screen and a frame mounting the shadow mask by supporting it about its periphery comprising an unbroken metallic loop generally conforming in contour with the periphery of said shadow mask disposed adjacent to said shadow mask and in contact with the periphery thereof, said metallic loop comprising two arms disposed from an intersection in a generally L-shaped cross section with one arm in contact with the periphery of the shadow mask and the other arm disposed away from the shadow mask and picture tube screen, said rim member comprising sintered porous material having at various positions about said periphery a thickness of the sintered porous material in the vicinity of the intersection of the two arms differing from that at the positions of the arms more remote from the intersection.
 2. Apparatus as defined in claim 1, in combination with a cathode ray picture tube having a phosphor screen disposed in a high vacuum.
 3. A frame as defined in claim 1, wherein the rim member is of a porous sintered metallic structure having a density in the order of 75 percent that of a solid metal.
 4. A frame member as defined in claim 1 with a one-piece rim member including bracket members extending outwardly therefrom. 